This invention relates generally to methods for delivering and collecting fluids, and, more particularly, to a method of using a multi-compartment assembly for delivering and collecting fluids used in calibrating an external apparatus.
Systems for measuring certain chemical characteristics of fluids, e.g., concentration of certain analytes such as ions, gases and metabolites in human blood, can take the form of blood chemistry diagnostic systems integrated into infusion fluid delivery systems of the kind commonly used in hospital patient care. Such fluid delivery systems infuse nutrients, medications and the like directly into the patient at a controlled rate and in precise quantities for maximum effectiveness. Infusion fluid delivery systems are connected to a patient at an intravascular (IV) port, in which a hollow needle/catheter combination, with an exposed female luer connector, is inserted into a blood vessel of the patient and thereafter an infusion fluid is introduced into the blood vessel at a controlled rate, typically using a peristaltic pump. Blood chemistry monitoring systems that are combined with infusion delivery systems of this kind use the IV port to periodically withdraw a blood sample, perform measurements of blood ion concentrations and the like, and then discard the blood or reinfuse it into the patient. The system then resumes delivery of the infusion fluid.
Such combined infusion fluid delivery and blood chemistry monitoring systems include an intravascular tube and catheter through which the infusion fluid is provided to the patient and blood samples are withdrawn. The intravascular tube incorporates an electrode array having sensors (e.g., electrochemical, optical, etc.) that are periodically exposed to the blood samples and thereby provide signals to an analyzer for conversion into corresponding blood chemistry data. A control unit periodically halts delivery of the infusion fluid for a brief interval, during which time a blood sample is withdrawn from the patient into the intravascular tube and routed to the sensor array, which then generates the electrical signals. After the electrical signals have been received by the analyzer, the control unit disposes of the blood or reinfuses it into the patient, and the flow of infusion fluid is resumed.
When electrochemical sensors are employed, the electrode array typically includes a reference electrode and a plurality of sensor electrodes that are each sensitive to a particular ion of interest. An example of an electrode array of this type is shown in U.S. Pat. No. 5,220,920. When an electrode array of this type is used to measure the concentration of various gases in a parent's blood, it is important that the electrode array be stabilized and that the infusion fluid have a temperature very close to the normal patient temperature. This ordinarily necessitates a lengthy stabilization and warm-up period prior to the infusion of fluids into the patient.
Accordingly, during the stabilization and warm-up period, typically about 30 minutes, the heated infusion fluid is passed through the electrode array and then discarded. Further, near the end of the period, a calibration fluid must be passed through the electrode array, to properly calibrate the sensor electrodes, and then discarded. Throughout this entire procedure, sterility must be maintained.
It should therefore be appreciated that there is a need for a method for supplying, collecting and storing calibration and infusion fluids that maintains a sterile environment through the warm-up and calibration process. The present invention fulfills this need.